If vanishing gradients are NOT the problem that ResNets solve, then what is the explanation behind ResNet success?
They explained in the paper why they introduce residual blocks. They argue that it's easier to learn residual functions $F(x) = H(x) - x$ and then add them to the original representation $x$ to get hidden representation $H(x) = F(x) + x$ than it is to learn hidden representation $H(x)$ directly from original representation. That's the main reason and empirical results show that they might be right. Better gradient propagation might be an additional bonus but that's not why they originally introduced the idea.
&quot;Normal&quot; networks work too but, at some point, they become too deep and start working worse than shallower versions (they empirically showed that in the paper). Again, they argue that the reason for that might be that at deeper layers hidden representations become approximately similar $H_n \approx H_{n+1}$ because representation is already well learned and you only need some slight adjustments.  That would mean that transformation for deeper layers is similar to identity transformation and that ordinary layers might have trouble learning that, while for residual blocks it would be easy to learn slight modification and add that to the already existing representation from the previous layer.